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SANTA CLARA — A small technology company said Wednesday it was expanding its patent infringement lawsuit against Microsoft Corp. and would try to stop sales of the new Windows XP operating system.

Microsoft said the suit was baseless and promised to fight it.

The lawsuit by InterTrust Technologies Corp. concerns digital rights management, or antipiracy measures that are essential in putting music, movies and other copyright material on the Internet. Digital rights management technology is used to limit what users can do with copyright material.

InterTrust first sued in April, claiming the digital rights management software in Microsoft’s Windows Media Player program and its operating systems violated a patent issued to InterTrust in February. That patent covers technology used in downloading digital content.

On Tuesday, InterTrust said it had been granted another patent, this one governing its process for securing content that is copied from one device to another, such as from personal computers to MP3 players.

The company said the new patent “substantially expands the implications for Microsoft’s current and future products” that also secure content being transferred between devices. Specifically, InterTrust cited Windows Media Player, and the Millennium Edition and upcoming XP version of the Windows operating system.

InterTrust said it would ask a federal court to stop sales of any Microsoft products that infringe on the patents.

“The underlying issue is Microsoft’s failure to respect InterTrust’s pioneering, inventive work,” said Ed Fish, president of the MetaTrust Utility, which is part of Santa Clara-based InterTrust.

Microsoft spokesman Jim Cullinan said he could not discuss the details of Microsoft’s digital rights management technology. But he said the lawsuit was “without merit” and mostly aimed at generating public-relations benefits for InterTrust.

InterTrust, founded in 1990, has licensing agreements and business partnerships with several companies that figure to play a large role in the future of digital content on the Internet, including AOL-Time Warner, Adobe Systems, Nokia, Universal Music Group and Blockbuster.

Shares of InterTrust lost 3 cents to $1.19 on the Nasdaq Stock Market, where Microsoft shares gained $1 to $71.14. InterTrust stock is well off its 52-week high of $25.50 and the $100 price it achieved before the dot-com bust in 2000.